Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS6251532 B1
Publication typeGrant
Application numberUS 08/555,415
Publication dateJun 26, 2001
Filing dateNov 9, 1995
Priority dateNov 11, 1994
Fee statusLapsed
Also published asUS6544672
Publication number08555415, 555415, US 6251532 B1, US 6251532B1, US-B1-6251532, US6251532 B1, US6251532B1
InventorsMasaaki Futamoto, Nobuyuki Inaba, Tomoo Yamamoto, Masukazu Igarashi, Yuzuru Hosoe, Akira Ishikawa
Original AssigneeHitachi, Ltd.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Multilayer; nonmagnetic substrate, magnetic layer, protective coatings
US 6251532 B1
Abstract
A magnetic recording medium capable of reducing noise and an error rate of the medium comprises a nonmagnetic substrate; a magnetic layer formed on the surface of the nonmagnetic substrate directly or through a nonmagnetic underlayer; and a protective layer formed on the magnetic layer. The magnetic recording medium satisfies the following relationships:
−0.5≦{Hc(1)−Hc(p)}/Hc(1)≦0.3
Hc(1)≧2 kOe
20 Gμm≦Br(1)t≦100 Gμm
where Hc(1) is a corecivity of the magnetic layer measured in the longitudinal direction; Hc(p) is a coercivity of the magnetic layer measured in the perpendicular direction; Br(1) is a remanent magnetization of the magnetic layer measured in the longitudinal direction; and t is a layer thickness of the magnetic layer.
Images(4)
Previous page
Next page
Claims(23)
What is claimed is:
1. A magnetic recording medium comprising:
a nonmagnetic substrate;
a magnetic layer formed on the surface of said nonmagnetic substrate directly or on a nonmagnetic underlayer which is formed directly on the surface of the nonmagnetic substrate; and
a protective layer formed on said magnetic layer;
wherein said magnetic recording medium satisfies the following relationships:
−0.5≦{Hc(1)−Hc(p)}/Hc(1)≦0.3
Hc(1)≧2 kOe
20 Gμm≦Br(1)t≦100 Gμm
Ku≧3106 erg/cm3
t≦20 nm
wherein Hc(1) is a coercivity of said magnetic layer measured in the longitudinal direction; Hc(p) is a coercivity of said magnetic layer measured in the perpendicular direction; Br(1) is a remanent magnetization of said magnetic layer measured in the longitudinal direction; Ku is a magnetic anisotropy energy of said magnetic layer; and t is a layer thickness of said magnetic layer.
2. A magnetic recording medium according to claim 1, wherein said magnetic layer is of a laminated structure comprising two or more magnetic layers having different compositions directly laminated to each other.
3. A magnetic recording medium according to claim 1, wherein said magnetic layer is of a laminated structure comprising two or more magnetic layers laminated to each other such that a nonmagnetic layer is interposed between each two of said magnetic layers.
4. A magnetic recording medium according to claim 1, wherein said magnetic layer is formed on a nonmagnetic underlayer, said nonmagnetic underlayer having a body centered cubic structure, and wherein said magnetic layer comprises a Co-based magnetic alloy layer having a hexagonal close-packed structure.
5. A magnetic recording medium according to claim 1, wherein said magnetic layer is composed of a mixture of crystal grains of a Co-based alloy having a hexagonal close-packed structure and a nonmagnetic material.
6. A magnetic recording medium according to claim 5, wherein an average grain diameter of said crystal grains of said Co-based alloy having a hexagonal close-packed structure is within the range of from 5 to 15 nm.
7. A magnetic recording medium according to claim 6, wherein a layer of said nonmagnetic material having a thickness of 0.3 nm or more is provided between said crystal grains.
8. A magnetic recording medium according to claim 1, wherein said magnetic layer is formed on said nonmagnetic underlayer.
9. A magnetic storage device comprising:
a magnetic recording medium a comprising nonmagnetic substrate;
a magnetic layer formed on the surface of said nonmagnetic substrate directly or on a nonmagnetic underlayer which is formed directly on the surface of the nonmagnetic substrate; and
a protective layer formed on said magnetic layer;
wherein said magnetic recording medium satisfies the following relationships:
−0.5≦{Hc(1)−Hc(p)}/Hc(1)≦0.3
Hc(1)≧2 kOe
20 Gμm≦Br(1)t≦100 Gμm
Ku≧3106 erg/cm3
t≦20 nm
wherein Hc(1) is a coercivity of said magnetic layer measured in the longitudinal direction; Hc(p) is a coercivity of said magnetic layer measured in the perpendicular direction; Br(1) is a remanent magnetization of said magnetic layer measured in the longitudinal direction; Ku is a magnetic anisotropy energy of said magnetic layer; and t is a layer thickness of said magnetic layer; and
a composite head comprising an inductive thin film head for magnetic recording and a magnetic head for reproducing utilizing magneto-resistance effect;
wherein magnetic recording or reproducing is carried out in a condition that a distance between facing surfaces of said composite head and a surface of said magnetic layer of said magnetic recording medium is in the range of from 0.02 to 0.08 μm.
10. A magnetic storage device according to claim 9, wherein a track width of said inductive thin film magnetic head for magnetic recording is in the range of 0.3 to 2 μm, and a maximum linear recording density is at least 100 kFCI.
11. A magnetic storage device comprising:
a magnetic recording medium comprising a nonmagnetic substrate;
a magnetic layer formed on the surface of said nonmagnetic substrate directly or on a nonmagnetic underlayer which is formed directly on the surface of the nonmagnetic substrate; and
a protective layer formed on said magnetic layer;
wherein said magnetic recording medium satisfies the following relationships:
−0.5≦{Hc(1)−Hc(p)}/Hc(1)≦0.3
Hc(1)≧2 kOe
20 Gμm≦Br(1)t≦100 Gμm
Ku≧3106 erg/cm3
t≦20 nm
wherein Hc(1) is a coercivity of said magnetic layer measured in the longitudinal direction; Hc(p) is a coercivity of said magnetic layer measured in the perpendicular direction; Br(1) is a remanent magnetization of said magnetic layer measured in the longitudinal direction; Ku is a magnetic anisotropy energy of said magnetic layer; and t is a layer thickness of said magnetic layer; and
a composite head comprising an inductive thin film head for magnetic recording and a magnetic head for reproducing utilizing magneto-resistance effect;
wherein said composite head is moved relative to said magnetic recording medium while in contact therewith.
12. A magnetic storage device according to claim 9, wherein said magnetic head for reproducing is a giant magneto-resistance effect head.
13. A magnetic storage device according to claim 10, wherein said magnetic head for reproducing is a giant magneto-resistance effect head.
14. A magnetic storage device according to claim 11, wherein said magnetic head for reproducing is a giant magneto-resistance effect head.
15. A magnetic storage device according to claim 9, wherein Ku≧3106 erg/cm3 a track density of said magnetic recording medium is at least 10 kTPI.
16. A magnetic storage device according to claim 10, wherein Ku≧3106 erg/cm3 a track density of said magnetic recording medium is at least 10 kTPI.
17. A magnetic storage device according to claim 11, wherein Ku≧3106 erg/cm3 a track density of said magnetic recording medium is at least 10 kTPI.
18. A magnetic storage device according to claim 9, wherein Ku≧3>106 erg/cm3 a track width of said inductive thin film head for magnetic recording is 0.3 to 2 μm.
19. A magnetic storage device according to claim 11, wherein Ku≧3106 erg/cm3 a track width of said inductive thin film head for magnetic recording is 0.3 to 2 μm.
20. A magnetic storage device according to claim 9, wherein a track width of said inductive thin film head for magnetic recording is 0.3 to 2 μm.
21. A magnetic storage device according to claim 11, wherein a track width of said inductive thin film head for magnetic recording is 0.3 to 2 μm.
22. A magnetic storage device according to claim 15, wherein a track width of said inductive thin film head for magnetic recording is 0.3 to 2 μm.
23. A magnetic storage device according to claim 17, wherein a track width of said inductive thin film head for magnetic recording is 0.3 to 2 μm.
Description
BACKGROUND OF THE INVENTION

The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium improved to be suitable for high density magnetic recording by reducing noise generated from the magnetic recording medium and to a magnetic storage device using the same.

Studies have been made on a magnetic recording medium formed of a continuous magnetic thin film for realizing high density magnetic recording. Specifically, such a magnetic recording medium is prepared by a method wherein a thin film made of a ferromagnetic metal, Co or Co-based alloy is formed on a substrate made of a nonmagnetic material such as aluminum or glass coated with a plastic film or NiP film by radio frequency sputtering, ion beam sputtering, vacuum evaporation, electric plating or chemical plating. In the magnetic recording medium thus prepared, a microstructure of a magnetic thin film is closely related to magnetic properties. As a result, various attempts have been made to improve a magnetic layer constituting a magnetic recording medium for enhancing magnetic recording density and reproduced output.

For a longitudinal magnetic recording medium, it has been conceived that an easy magnetization axis thereof is desirable to be parallel to a substrate. On the other hand, various methods have been known to provide an underlayer between a substrate and a magnetic layer for ensuring longitudinal magnetic anisotropy. For example, U.S. Pat. No. 4,654,276 discloses a method in which a layer made of W, Mo, Nb or V is used as an underlayer for a CoPt magnetic layer. U.S. Pat. No. 4,652,499 discloses a method in which a VCr or FeCr alloy material is used as an underlayer. Japanese Patent Laid-open No. Sho 63-106917 discloses a method in which a nonmagnetic layer made of Cr, Ho, Ti or Ta as an underlayer for a magnetic layer made of Co, Ni, Cr or Pt. U.S. Pat. No. 4,789,598 discloses a method in which Cr or a CrV alloy is effective as an underlayer for a CoPtCr layer.

When a Co-based alloy magnetic layer is formed on a substrate through an underlayer made of Cr or a Cr alloy by sputtering, the underlayer is first oriented in (100) or (110). In this case, when the Co-based alloy magnetic layer is formed on the (100) orientated layer, the easy magnetization axis thereof is parallel to the substrate; while when the Co-based alloy magnetic layer is formed on the (110) oriented layer, the easy magnetization axis thereof is substantially in parallel to the substrate, more specifically, it is inclined at about 30 relative to the surface of the substrate.

For improvement in an a real density of magnetic recording, it is required to reduce noise generated from a magnetic recording medium as well as to enhance resolution of magnetic recording. In particular, when a reproducing magnetic head of a magneto-resistance (MR) type being high in read-out sensitivity, it becomes important to reduce noise of a magnetic recording medium. The prior art magnetic recording medium of a type in which the easy magnetization axis thereof is oriented in the longitudinal direction has a disadvantage that it can improve resolution of magnetic recording; however, it has a difficulty in reducing noise thereof. In particular, for an areal recording density of magnetic recording increased to 1 Gb/in2 or more, the prior art magnetic recording medium is very difficult to reduce noise thereof.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic recording medium suitable for high density magnetic recording and a magnetic storage device using the same.

The present inventors have experimentally studied magnetic recording media suitable for high density magnetic recording and found that the above-described object can be achieved by the following methods.

Specifically, it was revealed that a magnetic recording medium being low in degree of orientation or being isotropic (containing a perpendicular magnetization component) is superior in noise reduction to a magnetic recording medium with the easy magnetization axis thereof oriented in the longitudinal direction. Such a magnetic recording medium is required to satisfy the following requirement:

−0.5≦{Hc(1)−Hc(P)}/Hc(1)≦0.3

where Hc(1) is a coercivity measured in the longitudinal direction, and Hc(p) is a coercivity measured in the perpendicular direction.

In this requirement, to realize high density magnetic recording having an areal recording density of 1 Gb/in2 or more, the corecivity Hc(1) is required to be 2 kOe or more and a product of a remanent magnetization Br and a layer thickness t is required to be within the range of from 20 to 100 Gμm. When Hc(1) is less than 2 kOe or Brt is more than 100 Gμm, resolution of magnetic recording fails to be enhanced. On the other hand, when Brt is less than 20 Gμm, a sufficient signal output cannot be obtained upon reproduction of a recording signal by the magnetic head, the magnetic recording medium is difficult to be operated as a magnetic storage device.

To obtain a magnetic recording medium capable of satisfying the above-described requirement, the magnetic recording medium is required to ensure a high coercivity Hc(1) while thinning the thickness of a magnetic layer to 20 nm or less. In general, for a magnetic layer having a thickness of 20 nm or less, it is difficult to ensure a high coercivity. Consequently, to ensure a high coercivity of a magnetic recording medium using a magnetic layer having a thickness of 20 nm or less, a magnetic anisotropy energy Ku of the magnetic layer is required to be 3106 erg/cm3 or more.

To obtain a high coercivity Hc(1) in a magnetic recording medium using a magnetic layer being thin in thickness, it is effective that the magnetic layer is of a laminated structure. Specifically, in the case where the thickness of a magnetic layer is limited for reducing the value of Brt to 100 Gμm or less, the coercivity Hc(1) can be increased using the magnetic layer of a laminated structure in which two kinds or more magnetic layers different in composition are directly laminated, as compared with a single magnetic layer. While being not clear, the reason for this is conceived that stress and strain are generated at each interface between the magnetic layers because of a slight difference in lattice constant therebetween, thus contributing to improvement in corecivity. In this case, nonmagnetic elements of alloy components constituting the magnetic layers are collected at the interface between the magnetic layers. As a result, magnetic coupling between a plurality of the magnetic layers is weakened, causing an effect in reducing noise generated from the magnetic recording medium.

To positively weaken magnetic coupling between a plurality of magnetic layers, it is effective to insert a nonmagnetic layer at each interface between two kinds or more of the magnetic layers different in composition.

Another method may be also adopted to form a nonmagnetic material between crystal grains of a magnetic thin layer, wherein a magnetic layer is formed by sputtering, using an alloy target made of a CoCr, CoPt, CoCrTa, or CoCrPt alloy placed with pellets of a nonmagnetic material such as SiO2, ZrO2, TiB2, ZrB2, MoSi2, LaB6, SiC, B4C, or B6Si. In this method, an average grain diameter of magnetic crystals constituting the magnetic thin layer becomes smaller and also a thin layer made of nonmagnetic material is interposed between the crystal grains of the magnetic thin layer. In the magnetic recording medium having such a structure, the magnetic coupling force between magnetic crystal grains can be reduced, and thereby noise of the medium can be reduced. To realize a high density magnetic recording having an areal recording density of 1 Gb/in2 or more, the average grain diameter of magnetic crystals of a magnetic layer is desirable to be within the range of from 5 to 15 nm.

As a magnetic head in combination with such a magnetic recording medium, a composite head or separate type head, combining a thin film ring head for recording and an magneto-resistance effect (MR) head high in reproduction sensitivity for reproduction, is desirable. To realize a high density magnetic recording having an areal recording density of 1 Gb/in2 or more, a linear recording density of 100 kFCI (Kilo-Flux Changes per Inch) or more is generally required, and in this case, a distance between the magnetic head and the surface of a magnetic film of a magnetic recording medium is required to be 0.08 μm or less. The smaller the distance, the better the high density recording. However, when the distance is 0.02 μm or less, the thickness of a protective layer and a lubricant layer provided on the surface of the magnetic layer becomes significantly thin. This is poor in usability in terms of tribological reliability.

To realize a high density magnetic recording having an areal recording density of 1 Gb/in2 or more, the track width of a magnetic head is also required to be made smaller. For a linear recording density of 100 kFCI, the track density must be 10 kTPI (kilo-Tracks per Inch) or more for ensuring the areal recording density of 1 Gb/in2 or more. In this case, the track pitch becomes about 2.5 μm or less. When a guard band of 0.5 μm is set between recording tracks, the track width of a magnetic head must be 2 μm or less. On the other hand, a magnetic head having a track width being 0.3 μm or less is difficult to be practically prepared. The track width of a magnetic head in combination with the magnetic recording medium is thus within the range of from 0.3 to 2.0 μm. To realize an areal density of 4 Gb/in2 or more, a giant magneto-resistance effect (G-MR) head being higher in sensitivity than the MR head is desirable to be used as the reproducing head.

According to the present invention, there can be provided a magnetic recording medium suitable for high density magnetic recording by reducing noise generated therefrom and suppressing an error rate thereof, and thereby a magnetic storage device having an areal recording density of 1 Gb/in2 or more can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a first embodiment of a magnetic recording medium of the present invention;

FIG. 2 is a graph showing the relationship between a condition for forming the magnetic recording medium shown in FIG. 1 and a coercivity of the medium;

FIG. 3 is a sectional view of a second embodiment of the magnetic recording medium of the present invention;

FIG. 4 is a sectional view of a third embodiment of the magnetic recording medium of the present invention;

FIG. 5 is a sectional view of a fourth embodiment of the magnetic recording medium of the present invention; and

FIG. 6 is a sectional view of a fifth embodiment of the magnetic recording medium of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to accompanying drawings.

EMBODIMENT 1

A magnetic recording medium having a structure shown in FIG. 1 was prepared using a glass substrate (diameter: 2.5 in.) in the following procedure.

A Cr layer 102 having a body centered cubic (bbc) structure was formed on a substrate 101 at a substrate temperature of 300 C. to a thickness of 100 nm by radio DC magnetron sputtering. In this layer formation, a pressure of Ar gas used for sputtering was changed within the range of from 10 to 50 mTorr. A Co-10 at % Cr-8 at % Pt layer 103 having a hexagonal close-packed (hcp) structure was formed on the Cr layer to a thickness of 7 nm, and subsequently a Co-5 at % Cr-21 at % Pt layer 104 was formed to a thickness of 10 nm.

The above layers were measured in terms of magnetic anisotropy energy using a magnetic torque meter. As a result, the magnetic anisotropy energy Ku of the Co-10 at % Cr-8 at % Pt layer 103 was 3.6106 erg/cm3, and the value Ku of the Co-5 at % Cr-21 at % Pt layer 104 was 4.3106 erg/cm3. The pressure of Ar gas upon formation of the magnetic layers was specified at 5 mTorr. A carbon layer serving as a protective layer 105 was formed on these magnetic layers to a thickness of 10 nm, and a lubricant layer was then formed to a thickness of 5 nm. A magnetic recording medium was thus prepared.

FIG. 2 is a graph showing the dependence of an Ar gas pressure on Hc(1) and Hc(p) of a magnetic recording medium prepared with an Ar gas pressure varied upon formation of a Cr layer. The Hc(1) and Hc(P) were measured using a vibrating sample magnetometer (VSM). For the Ar gas pressure of 28 mTorr or less, the relationship of Hc(1)≧Hc(p) was given. On the other hand, for the Ar gas pressure of 28 mTorr or more, the relationship of [Hc(1)≦Hc(p)] was given.

Each layer structure was then examined by X-ray diffraction. As a result, the Cr layer exhibited (110) preferred orientation. On the other hand, in the CoCrPt magnetic layer growing on the Cr layer, the easy magnetization axis thereof was oriented in the direction inclined by about 30 relative to the surface of the substrate when the Ar gas pressure was low; while the ratio of crystal grains having the easy magnetization axis oriented in the perpendicular direction was increased when the Ar gas pressure became higher. The microstructure of the magnetic layer was also examined by electron microscope. This showed that when the Ar gas pressure was more than 20 mTorr, gaps of 1 nm or more were present between magnetic crystal grains.

The value of Brt of the magnetic recording medium was 7510 Gμm. Magnetic recording/reproducing properties of the magnetic recording medium were then measured using a recording/reproducing separate type magnetic head. In this case, a distance between the magnetic head and the magnetic recording medium was set at 0.04 m. The measured results are shown in Table 1.

TABLE 1
sample a b c d e f g h
Hc(1) kOe 3.2 3.0 2.7 2.5 2.3 2.1 2.0 1.8
Hc(p) kOe 2.0 2.1 2.2 2.5 2.7 2.8 3.0 3.2
Hc(1) − Hc(p)/Hc(1) 0.38 0.30 0.19 0 −0.18 −0.33 −0.5 −0.78
resolution D50 kFCI 145 142 140 138 130 128 125 110
medium noise (relative value) 1.0 0.8 0.6 0.4 0.35 0.30 0.26 0.20
error rate 1 10−5 1 10−6 7 10−7 7 10−7 8 10−7 8 10−7 1 10−6 5 10−5

From Table 1, it becomes apparent that as the value of {Hc(1)−Hc(p)}/Hc(1) is decreased, resolution (D50kFCI, wherein D50 represents a resolution index which indicates a value of kFCI at which a reproduced output becomes 50% of that of the lowest recording density) of the recording is reduced and noise of the medium is also largely reduced. The magnetic recording/reproducing system was evaluated in terms of error rate at an areal recording density equivalent to 2 Gb/in2. As a result, a desirable error rate in the range of 110−6 or less was obtained when the value of {Hc(1)−Hc(p)}/Hc(1) was within the range of from −0.5 to 0.3.

EMBODIMENT 2

A magnetic recording medium having a structure shown in FIG. 3 was prepared using a glass substrate (diameter: 2.5 in.) in the following procedure.

A Cr-10 at % Ti layer 202 having a bcc structure was formed on a substrate 201 to a thickness of 10 nm at a substrate temperature of 350 C. by radio frequency DC magnetron sputtering. In this layer formation, an Ar gas pressure was specified at 30 mTorr. On the Cr-10 at % Ti layer 202, there were continuously formed layers: a Co-17 at % Cr-10 at % Pt-3 at % Ta layer 203 having a hcp structure (thickness: 7.5 nm), a Cr-10 at % Ti nonmagnetic layer 204 (thickness: 1 nm), a Co-17 at % Cr-10 at % Pt-3 at % Ta layer 205 (thickness: 7.5 nm), and a carbon layer 206 (thickness: 5 nm). A magnetic recording medium was thus prepared.

In this magnetic recording medium, the magnetic anisotropy energy Ku was 4106 erg/cm3, Hc(1) was 2.7 kOe, Hc(p) was 2.4 kOe, and Brt was 90 Gμm. The microstructure of the magnetic layer in this medium was examined using electron microscope, which gave the result that an average grain diameter of magnetic crystal grains of the magnetic layer was about 12 nm.

Recording/reproducing properties of the magnetic recording medium were examined in the same condition as in Embodiment 1. This showed that a desirable error rate in the range of 110−6 or less was obtained at an areal recording density of 2 Gb/in2.

EMBODIMENT 3

A magnetic recording medium having a structure shown in FIG. 4 was prepared using a glass substrate (diameter: 1.8 in.) in the following procedure.

A Cr-45 at % V layer 302 having a bcc crystal structure was formed on a substrate 301 to a thickness of 8 nm at a substrate temperature of 350 C. by radio frequency DC magnetron sputtering. In this layer formation, an Ar gas pressure was specified at 30 mTorr. On the Cr-45 at % V layer 302, there were continuously formed layers: a Co-17 at % Cr-12 at % Pt layer 303 (thickness: 5.5 nm), a ZrO2 nonmagnetic layer 304 (thickness: 1 nm), a SmCo alloy layer 305 (thickness: 4.5 nm), and a carbon layer 306 (thickness: 5 nm). A magnetic recording medium was thus prepared.

Each layer structure of this magnetic recording medium was examined. As a result, it was revealed that an average crystal grain diameter of the magnetic layer was 103 nm, and although an epitaxial growth relationship was present between the CrV layer and the CoCrPt magnetic layer, any epitaxial growth relationship was not present between two kinds of the magnetic layers. In this magnetic recording medium, the magnetic anisotropy energy Ku was 4.8106 erg/cm3, Hc(1) was 2.9 kOe, Hc(p) was 2.6 kOe, and Brt was 50 Gμm.

Recording/reproducing properties of the magnetic recording medium were examined in the same condition as in Embodiment 1. This showed that a desirable error rate in the range of 110−6 or less was obtained at an areal recording density of 3 Gb/in2.

EMBODIMENT 4

A magnetic recording medium having a structure shown in FIG. 5 was prepared using a glass substrate (diameter: 1.8 in.) in the following procedure.

A Cr-5 at % Nb layer 402 having a bcc structure was formed on a substrate 401 to a thickness of 12 nm at a substrate temperature of 320 C. by radio frequency DC magnetron sputtering. In this layer formation, an Ar gas pressure was specified at 15 mTorr. A magnetic layer 403 was formed on the Cr-5 at % Nb layer 402 to a thickness of 15 nm by DC magnetron sputtering. In this sputtering, there was used an alloy target made of a Co-14 at % Cr-12 at % Pt alloy having a hcp structure on which pellets of ZrO2 were placed at an area ratio of 12%. Then, a carbon layer 404 as a protective layer was continuously formed thereon to a thickness of 5 nm. A magnetic recording medium was thus prepared.

Each layer structure of this magnetic recording medium was examined. As a result, it was revealed that an average crystal grain diameter of the magnetic layer was 93 nm, and a nonmagnetic layer of ZrOx having a thickness of about 0.5 nm was present between magnetic crystal grains. In this magnetic recording medium, the magnetic anisotropy energy Ku was 3.2106 erg/cm3, Hc(1) was 2.2 kOe, Hc(p) was 1.6 kOe, and Brt was 58 Gμm.

Recording/reproducing properties of the magnetic recording medium were examined in the same condition as in Embodiment 1. This showed that a desirable error rate in the range of 110−6 or less was obtained at an areal recording density of 2 Gb/in2.

Even in the case where pellets of ZrO2 was replaced with either of pellets of SiO2, TiB2, ZrB2, MoSi2, LaB6, SiC, B4C, and B6Si, magnetic crystal grains were refined and a nonmagnetic layer having a thickness of 0.3 nm or more was formed between the magnetic crystal grains.

For the magnetic recording medium satisfying the following requirements,

Ku≧3106 erg/cm3,

Hc(1)≧2 kOe,

−0.5≦{Hc(1)−Hc(P)}/Hc(1)≦0.3, and

20 Gμm ≦Brt≦100 Gμm,

a desirable error rate in the range of 110−6 was obtained at an areal recording density of 2 Gb/in2.

EMBODIMENT 5

A magnetic recording medium having a structure shown in FIG. 6 was prepared using a glass substrate (diameter: 1.8 in.) in the following procedure.

A CoO nonmagnetic layer 502 having a NaCl structure was formed on a substrate 501 to a thickness of 12 nm at a substrate temperature of 100 C. by radio frequency magnetron sputtering. In this layer formation, a (Ar+O2) gas pressure was specified at 15 mTorr. A magnetic layer 503 was then formed on the CoO layer 502 to a thickness of 15 nm at a (Ar+O2) gas atmosphere by DC magnetron sputtering. In this sputtering, an alloy target made of a CoPt alloy having a hcp structure was used. A carbon layer 504 as a protective layer was continuously formed thereon to a thickness of 3 nm. A magnetic recording medium was thus prepared.

Each layer structure of this magnetic recording medium was examined. As a result, it was revealed that an average crystal grain diameter of the magnetic layer was 61 nm, and in the magnetic layer, magnetic crystal grains were mixed with nonmagnetic Co-o crystal grains. In this magnetic recording medium, the magnetic anisotropy energy Ku was 3.1106 erg/cm3, Hc(1) was 2.8 koe, Hc(p) was 3.1 kOe, and Brt was 45 Gμm.

Recording/reproducing properties of the magnetic recording medium were measured by sliding a recording/reproducing separate type head relative to the magnetic recording medium in a contact condition. The separate type head is composed of a thin film ring head having a track width of 0.8 μm and a high sensitivity reproducing head using a giant magneto-resistance effect film (G-MR film). A distance between the magnetic head and the surface of the magnetic recording medium was set at 0.03 μm. As the result, it was revealed that a desirable error rate in the range of 110−6 or less was obtained at an areal recording density of 8 Gb/in2.

As described above, in the present invention, a magnetic recording medium capable of reducing noise of the medium and an error rate can be provided, and thereby, a magnetic disk device having a recording density of 1 Gb/in2 or more can be realized. Therefore, it becomes possible to reduce the size of the magnetic disk device and to easily increase the capacity of the device.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4652499Apr 29, 1986Mar 24, 1987International Business MachinesMagnetic recording medium with a chromium alloy underlayer and a cobalt-based magnetic layer
US4654276Apr 29, 1986Mar 31, 1987International Business Machines CorporationCobalt-platinum alloy; tungsten, molybdenum, niobium, vanadium
US4746569 *May 14, 1986May 24, 1988Fujitsu LimitedLongitudinal magnetic coated recording medium
US4789598Jan 20, 1987Dec 6, 1988International Business Machines CorporationWith platinum and chromium for corrosion resistance, noise reduction; high density disks
US5147732 *Sep 26, 1989Sep 15, 1992Hitachi, Ltd.Composite magnetic film on a nonmagnetic substrate wherein magnetic thin metal films are coupled so as to have single plane coercivity
US5344706 *Nov 12, 1992Sep 6, 1994Carnegie Mellon UniversityMagnetic recording medium comprising an underlayer and a cobalt samarium amorphous magnetic layer having a SmCo5 crystalline interface with the underlayer
US5367411 *Aug 3, 1992Nov 22, 1994Hitachi, Ltd.Magnetic recording and reproducing apparatus with reproducing head of magnetoresistive type having control of magnetic bias level
US5408377 *Oct 15, 1993Apr 18, 1995International Business Machines CorporationMagnetoresistive sensor with improved ferromagnetic sensing layer and magnetic recording system using the sensor
US5442508 *May 25, 1994Aug 15, 1995Eastman Kodak CompanyGiant magnetoresistive reproduce head having dual magnetoresistive sensor
US5492774 *Jul 20, 1992Feb 20, 1996Sony CorporationPerpendicular magnetic recording medium and process for production of the same
US5492775 *May 28, 1993Feb 20, 1996International Business Machines CorporationBarium ferrite thin film for longitudinal recording
US5493466 *Jun 22, 1994Feb 20, 1996Sony CorporationComposite thin film recording/reproducing head with MR reproducing head having greater track width than recording head
US5597638 *Jan 13, 1994Jan 28, 1997Fuji Photo Film Co., Ltd.Magnetic recording medium
US5815343 *Oct 27, 1997Sep 29, 1998Hitachi, Ltd.Magnetic recording medium, process for producing the same and magnetic recording system
US5851643 *Mar 26, 1997Dec 22, 1998Hitachi, Ltd.Magnetic recording media and magnetic recording read-back system which uses such media
EP0330116A2 *Feb 20, 1989Aug 30, 1989Sony CorporationMagnetic recording medium
EP0488377A2 *Nov 29, 1991Jun 3, 1992Sony CorporationMagnetic recording medium and method of magnetically recording analog or, preferably, digital picture signals
Non-Patent Citations
Reference
1 *Bertram, Theory of Magnetic Recording, Cambridge Univ. Press, 1994, pp. 4,5, (no month).
2Mee, ed. Magnetic Recording Techology, 2nd Ed., Mcgraw Hill, pp. 3.10-3.15 (no date).*
3Velu et al., "Co-Sm based high coercivity . . . " J. Appl. Phys. 69(8), Apr. 15, 1991, pp 5175-5157.*
4Velu et al., "High Density Recording . . . " IEEE Trans. Magn. 28(5), Sep. 1992, pp 3249-3254.*
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6461750 *Sep 28, 1999Oct 8, 2002Seagate Technology, Inc.Magnetic recording medium with dual magnetic layers and high in-plane coercivity
US6544672 *Oct 3, 2000Apr 8, 2003Hitachi, Ltd.Magnetic recording medium and magnetic storage
US6671116 *Jan 15, 2002Dec 30, 2003Hitachi, Ltd.Magnetic recording system including magnetic recording medium having three-dimensional random orientation of axis of easy magnetization
US6723374Sep 24, 2002Apr 20, 2004Seagate Technology LlcSputtering using shield
US6893542Nov 1, 2002May 17, 2005Seagate Technology LlcSputtered multilayer magnetic recording media with ultra-high coercivity
US7242553 *Sep 7, 2004Jul 10, 2007Shin-Etsu Chemical Co., Ltd.Substrate for magnetic recording medium
US8208217 *Sep 30, 2008Jun 26, 2012Sony CorporationMagnetic recording medium and magnetic recording/reproducing system
Classifications
U.S. Classification428/828, 360/110, G9B/5.24, G9B/5.236, G9B/5.241, 360/131
International ClassificationG11B5/02, G11B5/39, G11B5/64, G11B5/738, G11B5/65, C22C27/06, G11B5/66
Cooperative ClassificationY10S428/90, G11B5/64, C22C27/06, G11B5/656, G11B5/66
European ClassificationG11B5/65B, G11B5/66, G11B5/64, C22C27/06
Legal Events
DateCodeEventDescription
Aug 23, 2005FPExpired due to failure to pay maintenance fee
Effective date: 20050626
Jun 27, 2005LAPSLapse for failure to pay maintenance fees
Jan 12, 2005REMIMaintenance fee reminder mailed
Nov 9, 1995ASAssignment
Owner name: HITACHI, LTD., JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:YAMAMOTO, TOMOO;INABA, NOBUYUKI;YAMAMOTO, TOMOO;AND OTHERS;REEL/FRAME:007762/0855
Effective date: 19951019